This invention relates in general to the working or fabrication of metals at high temperatures and, more particularly, to means for preventing metallurgical bonding between such metals and the working components of the fabrication equipment.
The problem of unwanted metallurgical bonding of alloys to pressing apparatus and other elements, such as the protective covering utilized around alloy powders in some instances, has long been recognized. Various compositions have been utilized in the past to minimize such bonding as described, for example, in the patent to Boucher et al. U.S. Pat. No. 3,380,917.
As processing temperatures rise, the potential for diffusion bonding typically becomes more acute. In forging processes such as that described in the patent to Moore et al. U.S. Pat. No. 3,519,503, a combination of high temperatures and hot dies, and a high ductility condition of the materials being forged, all tend to promote diffusion bonding between such materials and the working components of the forging press.
In an application copending herewith filed on May 10, 1971 for Forging Die Lubrication and assigned Ser. No. 141,530, the use of powdered boron nitride is suggested as one example of a suitable high temperature lubricant for forging operations. This lubricant minimizes the metallurgical bonding problem between the dies and the material being forged.
The use of lubricants in powder or paste form is not, however, the answer in some applications. First, powders are by their very nature susceptible to dislodgment due, for example, to a wiping action during handling or working and, in practice, reapplication of lubricant between working run is usually required on a periodic basis. The lubricant reapplication process may be particularly difficult where large heated components are involved.
Furthermore, in some applications where precise dimensional controls are required, the wiping action of the lubricant not only results in the scrubbing of lubricant from some areas but also in a buildup of lubricant in other areas. The net result is an inability to maintain a precise control of dimension where required. A lubricant buildup has, for example, been found to prevent the complete filling of a closed die cavity in the forging of components of complex contour. In another case where thin walled structures were being joined under pressure in a diffusion bonding operation between two flat platens, a lubricant buildup so interfered with the essential flatness of the platens that uneven deformation of the bonded members occurred.